Remove the macros, use the getters of `struct dynamic_prop` instead.
gdb/ChangeLog:
* gdbtypes.h (TYPE_LOW_BOUND, TYPE_HIGH_BOUND): Remove. Update
all callers to use type::range_bounds followed by
dynamic_prop::{low,high}.
Change-Id: I31beeed65d94d81ac4f999244a8b859e2ee961d1